This invention relates to combustion inhibitors for solid gas-generating compositions, especially but not exclusively solid propellants for rocket motors. Solid propellant rocket motors include a charge of propellant, an inhibitor on certain parts of the charge to control the area of burning surface, and an outer case. The inhibitor is used to control locally the burning area of the propellant so that the charge burns in the desired geometrical manner. The inhibitor needs to be chemically and physically compatible with the charge and may be completely or partially consumed during the firing of the rocket motor.
If a rocket motor emits smoke, the trail can betray the firing point of the missile and its trajectory. Further, exhaust smoke obscures the target and missile from the person firing the missile which is particularly disadvantageous if the missile is being visually guided along the line of sight to its target. Thus, frequently, one of the major requirements of a rocket motor is that stoke emission during combustion be as low as possible. As regards the propellant itself, this condition is met by the use of multiple base propellants, for example double base propellants comprising nitrocellulose and nitroglycerine or other liquid nitric acid ester which may contain additives such as chemical stabilisers, plasticisers and/or ballistic modifiers. Combustion of inert parts, largely the charge inhibitor, often, however, prevents the achievement of a "smokeless" exhaust.
Additionally, gas generating compositions, for example propellant charges or power cartridges, are widely used for mechanical operations and in such circumstances smoke condensate may be a nuisance because it can foul the area into which it is discharged and cause interference with valve mechanisms and moving surfaces.